Abstract
The Working Party on International Nuclear Data Evaluation Co-operation (WPEC) subgroup 29 (SG 29) was established to investigate an issue with the 235 U capture cross-section in the energy range from 0.1 to 2.25 keV, due to a possible overestimation of 10% or more. To improve the 235 U capture crosssection, a new 235 U evaluation has been proposed by the Institut de Radioprotection et de Surete Nucleaire (IRSN) and the CEA, mainly based on new time-of-flight 235 U capture cross-section measurements and recent fission cross-section measurements performed at the n_TOF facility from CERN. IRSN and CEA Cadarache were in charge of the thermal to 2.25 keV energy range, whereas the CEA DIF was responsible of the high energy region. Integral experiments showing a strong 235 U sensitivity are used to assess the new evaluation, using Monte-Carlo methods. The k eff calculations were performed with the 5.D.1 beta version of the MORET 5 code, using the JEFF-3.2 library and the new 235 U evaluation, as well as the JEFF-3.3T1 library in which the new 235 U has been included. The benchmark selection allowed highlighting a significant improvement on k eff due to the new 235 U evaluation. The results of this data testing are presented here.
Highlights
Institut de Radioprotection et de Surete Nucleaire (IRSN) has carried out benchmark calculations, using few-selected benchmarks extracted from the International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook [8] for testing the new 235U evaluation over the whole energy range
The results clearly indicate a discrepancy compared to full JEFF-3.2 results with a strong improvement in the intermediate energy range
IRSN and CEA have produced a new evaluation for 235U in the thermal to fast energy range
Summary
Integral quantities, such as fission and capture resonance integral and Westcott factors were included in the evaluation. The CEA DIF was in charge of the evaluation at high energy and recommendations done by the CIELO organization [6, 7] concerning the 235U PFNS (prompt fission neutron spectrum) among others, were followed. A common IRSN-CEA evaluation called “u235 irsncea 1” was released. IRSN has carried out benchmark calculations, using few-selected benchmarks extracted from the International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook [8] for testing the new 235U evaluation over the whole energy range. The impact of the inclusion of the new evaluation was studied for selected critical benchmarks sensitive to the 235U capture cross-section in the thermal, epithermal and fast energy ranges.
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